Optical light pipe with uniform lit intensity

ABSTRACT

The present application discloses a light pipe assembly having a light pipe with a proximal end, an opposing distal end, a length between the proximal end and the distal end, and a surface, the surface having an emitting portion and an overlay portion, where the light pipe is a material capable of transmitting light with a first refractive index; and a reflective secondary surface having a second refractive index and a width, the reflective secondary surface positioned adjacent the overlay portion of the light pipe, where the first refractive index is greater than the refractive index of air, and the second refractive index is greater than the first refractive index. In at least one embodiment, the reflective secondary surface is a non-metallic material capable of reflecting light. In at least one embodiment, the width of the reflective secondary surface varies along the length of the light pipe.

PRIORITY

This application is related to, and claims the priority benefit of, andis a U.S. continuation application of, U.S. Nonprovisional patentapplication Ser. No. 13/840,425, filed Mar. 15, 2013 and issued as U.S.Pat. No. 9,677,721 on Jun. 13, 2017, which is related to, and claims thepriority benefit of U.S. Provisional Patent Application Ser. No.61/745,298, filed Dec. 21, 2012. The contents of each of the foregoingpatent applications are hereby incorporated by reference in theirentirety into this disclosure.

BACKGROUND

The design of the exterior lighting components of automobiles plays animportant role in the styling and marketing of vehicles in theautomotive market. Vehicle designers are interested in technologies thatcan both provide the required regulatory functions of automotiveexterior lighting and enable a unique and aesthetically pleasing lit andunlit appearance of the lighting components on the vehicle. There isalso a desire to create uniformity and continuity in the lit appearanceof functionally separate lamps that may be in close proximity to oneanother, for instance, the corner tail lamp and the applique or liftgate lamps. Achieving the desired uniformity generally requires the useof the same light source in different lamps with different functions.Accordingly, potential light sources must be capable of providing arange of different automotive lighting functions.

In addition to the use of conventional incandescent bulbs in exteriorlighting, automotive engineers have more recently incorporated lightemitting diodes into lighting as a light source. Because light emittingdiodes are a point source generally providing light in a Lambertiandistribution, the use of light emitting diodes yields a lit appearancethat is “spotty” or “dotted,” which is currently common on manyautomobiles. However, more recently vehicle designers have demandedgreater homogeneity in the lit appearance of the lamps. Consequently, auniformly lit “neon-look,” similar to the appearance of a neon tube, isin relatively high demand. However, neon tubes have not been widelyadopted in automotive lighting due to a number of technical drawbacks.

Recently, light guides have been used in lamps to approximate the lookof a neon tube. However, conventional light guides or pipes havedifficulty creating a uniformly lit appearance because the emission oflight near the light source is generally significantly greater than thelight emission further along the length of the guide. The result is lineor bar of light that is noticeably brighter at an end than in themiddle.

Therefore, there is a need for an optical-grade light pipe that may belit with a single, localized source that provides a uniform lightintensity along its entire length and that enables a lamp meeting thefunctional requirements for an automotive lamp.

BRIEF SUMMARY

According to one aspect of the present disclosure a light pipe assemblyis disclosed. In at least one embodiment, a light pipe assembly includesa light pipe having a proximal end, an opposing distal end, a lengthbetween the proximal end and the distal end, and a surface, the surfacehaving an emitting portion and an overlay portion, where the light pipeis a material capable of transmitting light with a first refractiveindex; and a reflective secondary surface has a second refractive indexand a width, the reflective secondary surface disposed adjacent theoverlay portion of the light pipe, where the first refractive index isgreater than the refractive index of air, and the second refractiveindex is greater than the first refractive index. In at least oneembodiment, the reflective secondary surface is a non-metallic materialcapable of reflecting light.

In at least one embodiment, the reflective secondary surface is disposedadjacent the overlay portion of the light pipe such that a gap is formedbetween the reflective secondary surface and the light pipe, the gapselected such that the reflective secondary surface is capable ofpropagating an evanescent wave at a point where any of a plurality oflight rays traveling through the light pipe are internally reflected ata boundary between the overlay portion and reflective secondary surface.In at least one embodiment, the gap is variable along the length of thelight pipe.

In at least one embodiment, the width of the reflective secondarysurface varies along the length of the light pipe. In at least oneembodiment, the width of the reflective secondary surface is wider at ornear the distal end than at or near the proximal end of the light pipe.In at least one embodiment, the width of the reflective secondarysurface is narrower at or near the proximal end and at or near thedistal end of the light pipe than along the length therebetween. In atleast one embodiment, the light pipe includes a bend, and wherein thereflective secondary surface is narrower at or near the bend than at alocation adjacent thereto.

In at least one embodiment, the light pipe assembly further includes atleast one light source disposed adjacent the proximal end of the lightpipe, the at least one light source capable of generating a plurality oflight rays, wherein the plurality of light rays are generally directedinto the light pipe in the direction of the distal end. In at least oneembodiment, the light pipe assembly further includes at least one lightsource disposed adjacent the distal end of the light pipe, the at leastone light source capable of generating a plurality of light rays,wherein the plurality of light rays are generally directed into thelight pipe in the direction of the proximal end. In at least oneembodiment, the at least one light source is a light emitting diode.

In at least one embodiment, the light pipe assembly further includescoupling optics disposed between the at least one light source and thelight pipe. In at least one embodiment, the overlay portion of the lightpipe has a cross-sectional area having a first shape and the emittingportion of the light pipe has a cross-sectional area having a different,second shape.

According to one aspect of the present disclosure, a lamp assembly isdisclosed. In at least one embodiment, the lamp assembly includes alight pipe having a proximal end, an opposing distal end, a lengthbetween the proximal end and the distal end, and a surface, the surfacehaving an emitting portion and an overlay portion, where the light pipeis comprised of a material capable of transmitting light with a firstrefractive index; and at least one light source disposed adjacent theproximal end of the light pipe and capable of generating a plurality oflight rays, wherein the plurality of light rays are generally directedinto the light pipe in the direction of the distal end. The lampassembly further includes a reflective secondary surface having a secondrefractive index and a width, the reflective secondary surface disposedadjacent the overlay portion of the light pipe such that the reflectivesecondary surface is capable of propagating an evanescent wave at apoint where any of the plurality of light rays traveling through thelight pipe is internally reflected at a boundary between the overlayportion and reflective secondary surface, where the first refractiveindex is greater than the refractive index of air, and the secondrefractive index is greater than the first refractive index. The lampassembly further includes a housing and a lens, where the lens isdisposed adjacent the housing such that the lens and housingsubstantially surround the at least one light source, the light pipe,and the reflective secondary surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a rear view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 1B shows a side view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 2 shows a side view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 3A shows a cross-sectional view of an embodiment of an exemplaryoptical light pipe assembly according to the present disclosure;

FIG. 3B shows a cross-sectional view of an embodiment of an exemplaryoptical light pipe assembly according to the present disclosure;

FIG. 4A shows a rear view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 4B shows a side view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 5 shows a rear view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 6A shows a rear view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 6B shows a rear view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 7A shows a rear view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 7B shows a side view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 8 shows an iso-candela plot of the emitted light distribution of anembodiment of an exemplary optical light pipe assembly according to thepresent disclosure;

FIG. 9 shows an iso-candela plot of the emitted light distribution of anembodiment of an exemplary optical light pipe assembly according to thepresent disclosure;

FIG. 10 shows an iso-candela plot of the emitted light distribution ofan embodiment of an exemplary optical light pipe assembly according tothe present disclosure;

FIG. 11A shows a side view of an embodiment of an exemplary opticallight pipe assembly according to the present disclosure;

FIG. 11B shows a rear view of an embodiment of an exemplary opticallight pipe assembly according to the present disclosure;

FIG. 12 shows a rear view of an embodiment of an exemplary optical lightpipe assembly according to the present disclosure;

FIG. 13 shows a partially cutaway perspective view of an embodiment ofan exemplary optical light pipe assembly according to the presentdisclosure;

FIG. 14A illustrates total internal reflection of a light ray within amaterial according to the prior art; and

FIG. 14B illustrates evanescent coupling of a light ray at a mediaboundary according to the prior art.

DETAILED DESCRIPTION

The present application discloses various embodiments of anoptical-grade light pipe and methods for using and constructing thesame. According to one aspect of the present disclosure, a solidoptical-grade light pipe with a custom secondary reflective layer thatenables a uniform emitted light intensity along its length that may belit with a single localized source is disclosed. For the purposes ofpromoting an understanding of the principles of the present disclosure,reference will now be made to the embodiments illustrated in thedrawings, and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of thisdisclosure is thereby intended.

For the purposes of this disclosure, the terms light guide and lightpipe are equivalent. The efficiency of a light guide may be quantifiedas the total amount of light emitted from an emitting surface of theguide compared to the total light emitted by a light source coupled tothe guide.

FIG. 1A shows an optical light pipe assembly 10 according to at leastone embodiment of the present disclosure. As shown in FIG. 1A, the lightpipe assembly 10 may include a light pipe 20, having a proximal end 22,a distal end 24, and a surface 26, and a reflective secondary surface 40disposed adjacent the surface 26. The surface 26 may include an emittingportion 28 and an overlay portion 27, where the reflective secondarysurface 40 may be disposed adjacent the overlay portion 27 of thesurface 26. The light pipe assembly 10 may further include at least onelight source 30 optically coupled to the light pipe 20 at or near theproximal end 22 such that a plurality of light rays 32 may betransmitted into the light pipe 20 in the general direction of thedistal end 24.

As shown in FIG. 1A, the reflective secondary surface 40 may not becoextensive with the surface 26. Specifically, the area of thereflective secondary surface 40 may vary from a proximal end 42 near thelight source 30 to a distal end 44 further from the light source 30,generally corresponding to the proximal end 22 and the distal end 24 ofthe light pipe 20, respectively. More specifically, the width of thereflective secondary surface 40 may vary along the light pipe 20 fromthe proximal end 22 toward the distal end 24, such that the reflectivesecondary surface 40 may be wider at or near the distal end 44 furtherfrom the light source 30 and taper or become narrower at or near theproximal end 42 near the light source 30. Further, the reflectivesecondary surface 40 may be disposed adjacent the surface 26 such that agap 36 is maintained therebetween as shown in FIG. 1B. The magnitude ofthe gap 36 as depicted in FIG. 1B relative to the size of the reflectivesecondary surface 40 and the light pipe 20 has been exaggerated forclarity. The reflective secondary surface 40 may further extend to andbe disposed adjacent the distal end 24 of the light pipe 20. In such anembodiment, any of the plurality of light rays 32 incident upon thedistal end 24 may be reflected in the general direction of the proximalend 22 and, thus, contribute to the emitted light distribution of thelight pipe assembly 10.

In operation, the light pipe assembly 10 may produce a desired emittedlight distribution of substantially uniform intensity using totalinternal reflection and evanescent coupling. FIG. 14A illustrates theprinciple of total internal reflection according to the prior art. Totalinternal reflection is a phenomenon of light when it intersects aboundary between different media. As shown in FIG. 14A, an individuallight ray 95 propagating through a first medium 90, having a refractiveindex n₁, may fall incident upon a surface 93 at an angle of incidenceθ_(i), where the surface 93 forms a boundary 91 with a second medium 92,having a refractive index n₂. The angle of incidence θ_(i) may bedefined in relation to the normal of the surface 93 at the point wherethe light ray 95 is incident upon the surface 93.

The light ray 95 incident upon the surface 93 at an angle of incidenceθ_(i) will be partially refracted at the boundary 91 and partiallyreflected within the first medium 90. Where reflected, the light ray 95may reflect off the boundary 91 and remain in the first medium 90. Whererefracted, as shown in FIG. 14B, the light ray 95 may pass through thesurface 93 and emit from the first medium 90. Whether the light ray 95is reflected or refracted depends upon the angle of incidence θ_(i) therefraction index n1 of the first medium 90, and the refraction index n₂of the second media 92 as defined by Snell's Law:

n ₁(sin θ_(i))=n ₂(sin θ₂),

where θ₂ is the angle of the light ray after intersecting the boundary91 relative to the normal of the surface intersected.

According to Snell's Law, where the n₁ is greater than n₂ (that is,where the first medium 90 has a higher refractive index than the secondmedium 92), there exists a critical angle θ_(c) at which all light rays95 having an angle of incidence θ_(i) greater than the critical angleθ_(c) will be entirely reflected within the first medium 90. Thecritical angle is given by:

θ_(c)=arcsin(n ₂ /n ₁)

The reflection of all light rays 95 with an angle of incidence θ_(i) atthe boundary greater than the critical angle θ_(c) is known as totalinternal reflection. Where the fraction n₂/n₁ is greater than 1, thearcsine is not defined, meaning that total internal reflection does notoccur. Accordingly, the critical angle θ_(c) is only defined for n₂/n₁less than 1, meaning the refractive index n₁ of the first medium 90 mustbe greater than the refractive index n₂ of the second medium 92 toachieve total internal reflection.

At every point along the boundary 91 where total internal reflectionoccurs, a standing electromagnetic field called an evanescent wave 98 iscreated because the electric and magnetic fields associated with thelight ray 95 cannot be discontinuous at the boundary 91. Essentially,though total internal reflection occurs, an aspect of the incident lightray 95 is transmitted through the boundary 91 as a non-traveling or“standing” wave, the only solutions of which in a dielectric materialare those that decay exponentially. The resulting standing wave is knownas an evanescent wave.

As shown in FIG. 14B, the evanescent wave 98 may be made to propagate aspropagating ray 99 through a third medium 94 via evanescent coupling,where a refractive index n₃ of the third medium 94 is greater than therefractive index n₁ of the first medium 90, and where the third medium94 is positioned in close proximity to the first medium 90 at a pointwhere total internal reflection of the light ray 95 occurs. Thephenomenon of light in which the evanescent wave is made to propagatethrough the third medium 94 is referred to as evanescent coupling.

In at least one embodiment according to the present disclosure, thelight pipe assembly 10 is engineered to use the principles of totalinternal reflection and evanescent coupling of the light rays 32 fromthe light source 30 traveling through the light pipe 20 to generate anemitted light distribution that is of greater intensity and uniformitythan a conventional light guide. As shown in FIG. 2, in at least oneembodiment according to the present disclosure, the reflective secondarysurface 40 may be positioned adjacent the overlay portion 27 of thesurface 26 to form the gap 36 therebetween. The gap 36 may be selectedto enable the propagation of an evanescent wave 38 at the overlayportion 27. Because the evanescent wave 38 decays exponentially at adistance from the surface 26, the gap 36 may be very small. In at leastone embodiment, the gap 36 may be selected to position the reflectivesecondary surface 40 within several wavelengths of the light ray 32 fromthe overlay portion 27 of the surface 26. In at least one embodiment,the surface irregularities between the light pipe 20 and the reflectivesecondary surface 40 resulting from conventional manufacturing processesmay be sufficient to form the appropriate gap 36.

The light source 30 may be coupled to the light pipe 20 such that theplurality of light rays 32 emitted from the light source 30 travelsubstantially axially through the light pipe 20 in the general directionof the distal end 24. The plurality of light rays 32 may be internallyreflected within and along at least a portion of the light pipe 20 andeventually refracted through the surface 26 of the light pipe 20 as aplurality of emitted light rays 34 when the angle of incidence θ_(i) isbelow the critical angle θ_(c).

Where a light ray 32 is internally reflected at the overlay portion 27of the surface 26, the evanescent wave 38 may be generated at theboundary with the reflective secondary surface 40 as shown in FIG. 2.The evanescent wave 38 may then be reflected by the reflective secondarysurface 40 across the gap 36 and into the light pipe 20 as an evanescentray 33. The path of the reflected evanescent ray 33 will generally bedifferent than that of the internal reflected light ray 32 due torefraction at the boundary with the overlay portion 27. Consequently,the angle of incidence of the evanescent ray 33 will generally bedifferent than that of the light ray 32 upon intersecting the emittingportion 28 of the surface 26. As a result, the evanescent ray 33 may berefracted through the emitting portion 28 as an emitted light ray 34instead of internally reflected as may be the light ray 32. Bygenerating, refracting, and then emitting a plurality of evanescent rays33 from the surface 26, the light pipe 20 makes use of light energygenerally lost at each incidence of total internal reflection of theplurality of light rays 32 along the surface 26, thereby enablingincreased efficiency over conventional optical light guides.

In addition to generating, refracting, and then emitting the pluralityof evanescent rays 33 from the surface 26, the light pipe 20 furtherincreases efficiency by recapturing and subsequently emitting light rays34 that are refracted through the overlay portion 27 of the surface 26.Because the reflective secondary surface 40 is reflective, light rays 32that are refracted through the overlay portion 27 and emitted as emittedrays 34 may be reflected back into the light pipe 20 as reflected rays35 as shown in FIG. 2. Similar to the evanescent ray 33, the path of thereflected ray 35 will generally be different than that of the internalreflected light ray 32 due to the refraction at the boundary of theoverlay portion 27. Consequently, the angle of incidence of thereflected ray 35 will generally be different than that of the light ray32 upon intersecting the emitting portion 28 of the surface 26. As aresult, the reflected ray 35 may be refracted through the emittingportion 28 as an emitted light ray 34 instead of internally reflected,as may be the light ray 32. Alternatively, the reflected ray 35 mayundergo additional internal reflection upon intersecting the surface 26,thereby propagating further along the axis of the light pipe 20.

Consequently, the efficiency of the optical light pipe assembly 10according to the present disclosure is improved over conventional lightpipes that do not include the reflective secondary surface 40 adjacentthe overlay portion 27 of the surface 26. First, light rays 32 that havean angle of incidence θ₁ upon the surface 26 greater than the criticalangle θ_(c) may be reflected internally within the light pipe 20 andeventually emitted through the emitting surface 28. Second, light rays32 that have an angle of incidence θ_(i) less than the critical angleθ_(c) may be refracted through the surface 26. The light rays 32refracted at the overlay portion 27 may travel across the gap 36, bereflected by the reflective secondary surface 40 back into the lightpipe 20, and eventually emitted through the emitting surface 28 as shownin FIG. 2. Third, light energy that could be lost at a point of totalinternal reflection may be converted to a propagating evanescent wave 38that may be reflected by the reflective secondary surface 40 back intothe light pipe 20 and eventually emitted through the emitting surface28, which further contributes to the intensity of the light emitted fromthe light pipe 20.

The width or area of the reflective secondary surface 40 may be variedto affect the intensity and uniformity of the emitted light distributionand, thereby, the lit appearance along the length of the light pipe 20.In at least one embodiment, the width of the reflective secondarysurface 40 may generally increase as the distance from the light source30 increases to maintain uniform intensity of the emitted lightdistribution along the length of the light pipe 20. The change in widthof the reflective secondary surface 40 need not be linear or constant.Likewise, the width of the reflective secondary surface 40 may decreaseas the distance from the light source 30 increases as needed to maintainuniform intensity of the emitted light distribution along the length ofthe light pipe 20 as described herein. Thus, the positioning,configuration, and properties of the reflective secondary surface 40relative to the light pipe 20 enable the optical light pipe assembly 10to produce the desired intensity of light with the desired aestheticappearance effectively and efficiently. For example, in one exemplaryembodiment of a light pipe assembly 10 having a length for 27 inches(in.) (689 millimeters (mm)), the width of the reflective secondarysurface 40 may remain relatively narrow and increase very slowly up to adistance approximately 14 in. (356 mm) from the light source 30, wherethe width of the reflective secondary surface 40 may then increaserapidly over the remaining length of the light pipe 20.

The geometry of the light pipe 20 may be varied according to the desiredlit appearance of the light pipe assembly 10. As shown in FIG. 3A, thelight pipe 20 may have a circular cross-sectional area of radius R,which may enable the most efficiently reflecting overlay portion 27. Thelight pipe 20 may have other cross-sectional shapes, including but notlimited to elliptical and parabolic. Further, the light pipe 20 mayincorporate more than one cross-sectional shape. As shown in FIG. 3B,the light pipe 20 may include a circular reflecting overlay portion 27of radius R and an elliptical emitting portion 28 of radius R′. Thelight pipe 20 may have any suitable cross-sectional configurationdepending upon the desired lit appearance of the light pipe assembly 10.

FIGS. 4A and 4B show the light pipe assembly 10 according to at leastone embodiment of the present disclosure. The light pipe assembly 10 mayinclude more than one light source 30 each disposed at or near both theproximal end 22 and the distal end 24 of the light pipe 20 having thereflective secondary surface 40 disposed adjacent thereto. As shown inFIG. 4A, the reflective secondary surface 40 may varying in width suchthat the reflective secondary surface 40 is tapered or narrow at or neareach light source 30 and wider at a position between the proximal end 22and the distal end 24. Consequently, the light pipe assembly 10 mayincorporate a plurality of light sources 30, and the reflectivesecondary surface 40 may vary in width accordingly to enable theintensity and uniformity of emitted light rays 34 to form the desiredlit appearance of the light pipe assembly 10.

In at least one embodiment according to the present disclosure, thelight pipe 20 may not be entirely straight and may include at least onecurved portion 29 as shown in FIG. 5. At a curved portion 29, light rays32 may be more likely to exit the light pipe 20 via the emitting surface28 due to the changing angles of incidence θ_(i) corresponding to thechange in geometry and form of the surface 26 of the light pipe 20.Consequently, because light tends to “bleed” or escape the light pipe 20at or near the curved portion 29, the width of the reflective secondarysurface 40 may be decreased at or near the radius of the curved portion29 to enable and maintain the desired intensity of emitted light.

In at least one embodiment according to the present disclosure, thelight pipe 20 may include a reflective secondary surface 40 formed ofand defined by a plurality of spaced bands 46 spanning the width of thereflective secondary surface 40 as shown in FIG. 6A. In at least oneembodiment, the spaced bands 46 defining the reflective secondarysurface 40 may be closely spaced. The spacing of the spaced bands 46 maybe adjusted to affect the intensity and uniformity of the emitted lightdistribution emitted from the light pipe 20. Consequently, the lightpipe assembly 10 may include various configurations of spaced bands 46to enable the intensity and uniformity of emitted light rays 34 to formthe desired lit appearance of the light pipe assembly 10.

In at least one embodiment according to the present disclosure, thelight pipe 20 may include a reflective secondary surface 40 formed by aplurality of reflective dots 48 defining the reflective secondarysurface 40 as shown in FIG. 6B. In at least one embodiment, theplurality of reflective dots 48 defining the reflective secondarysurface 40 may be closely spaced. The spacing or density of theplurality of reflective dots 48 may be adjusted to affect the intensityand uniformity of the emitted light distribution emitted from the lightpipe 20. Consequently, the light pipe assembly 10 may include variousconfigurations of the plurality of reflective dots 48 to enable theintensity and uniformity of emitted light rays 34 to form the desiredlit appearance of the light pipe assembly 10. In at least onealternative embodiment, the reflective secondary surface 40 may becomprised of other suitable patterns in addition to the spaced bands 46or reflective dots 48.

In at least one embodiment according to the present disclosure, thelight pipe 20 may include a plurality of pipe optical elements 25 formedin the overlay portion 27 of the surface 26 as shown in FIGS. 7A and 7B.The pipe optical elements 25 may be formed to further affect theintensity and uniformity of the emitted light distribution from thelight pipe 20 by altering the angle of incidence, and therebyrefraction, of incident light rays 32. The reflective secondary surface40 may be disposed adjacent the plurality of pipe optical elements 25 onthe surface 26. In at least one embodiment, the plurality of pipeoptical elements 25 may be formed such that the plurality of pipeoptical elements 25 protrude from the surface 26 as shown in FIG. 7B.However, where the pipe optical elements 25 are relatively large, asignificant number of light rays 32 may be emitted near the light source30. Accordingly, in at least one embodiment as shown in FIG. 7A, thereflective secondary surface 40 may be disposed at or near the proximalend 22 near the light source 30 where no pipe optical elements 25 areformed. In such an embodiment, the reflective secondary surface 40 maynot extend over the area including the pipe optical elements 25. In atleast one exemplary embodiment, where the pipe optical elements 25 arerelatively small, the pipe optical elements 25 combined with thereflective secondary surface 40 may enable a 5-10% increase in the totallight emitted.

FIG. 8 depicts an iso-candela plot of empirical data of an emitted lightdistribution of at least one embodiment of the present disclosure. Inone exemplary embodiment, the light pipe assembly 10 may include thelight pipe 20 having a length of 3 in. (76.2 mm), a circularcross-sectional area having a diameter of 0.375 in. (9.525 mm), and thetapered reflective secondary surface 40 having a maximum width of 0.25in. (6.35 mm) at or near the distal end 44 and a minimum width of 0.0039in. (0.10 mm) at or near the proximal end 42. As shown in FIG. 8, suchan embodiment may produce an emitted light distribution having anangular spread of about 35 degrees up and down and about 65 degrees leftand right.

FIG. 9 depicts an iso-candela plot of empirical data from an emittedlight distribution of at least one embodiment of the present disclosure.In one exemplary embodiment, the light pipe assembly 10 may include thelight pipe 20 having a length of 3 in. (76.2 mm), an ellipticalcross-sectional area having a width along its major axis of 0.375 in.(9.525 mm) and a height along its minor axis of 0.25 in. (6.35 mm), andthe tapered reflective secondary surface 40 having a maximum width of0.25 in. (6.35 mm) at or near the distal end 44 and a minimum width of0.0039 in. (0.10 mm) at or near the proximal end 42. As shown in FIG. 9,such an embodiment may produce an emitted light distribution having anangular spread of about 60 degrees up and down and greater than 80degrees left and right.

FIG. 10 depicts an iso-candela plot of empirical data from an emittedlight distribution of at least one embodiment of the present disclosure.In one exemplary embodiment, the light pipe assembly 10 may include thelight pipe 20 having a length of 3 in. (76.2 mm), an ellipticalcross-sectional area having a width along its major axis of 0.50 in.(12.7 mm) and a height along its minor axis of 0.125 in. (3.18 mm), andthe tapered reflective secondary surface 40 having a maximum width of0.25 in. (6.35 mm) at or near the distal end 44 and a minimum width of0.0039 in. (0.10 mm) at or near the proximal end 42. As shown in FIG.10, such an embodiment may produce an emitted light distribution havingan angular spread of greater than 80 degrees up and down and greaterthan 80 degrees left and right.

The light pipe 20 may be formed of an optical-grade material, meaningthe material may have a transmissivity greater than 90% and exhibit verylow absorption over the useable, desired, visible wavelengths. Forexample, the light pipe 20 may be formed of glass, quartz,polymethylmethacrylate (i.e., acrylic), polycarbonate, silicone, or anyother suitable optical-grade material. The reflective secondary surface40 may be formed of any material having a higher refractive index thanthat of the light pipe 20 and having a sufficient reflectivity to enablethe prescribed intensity and uniformity of light emitted by the lightpipe 20.

The reflective secondary surface 40 may be formed of a reflectivenon-metallic material having a refractive index greater than therefractive index of the light pipe 20 to enable evanescent coupling ateach point of total internal reflection. Further, the reflectivesecondary surface 40 may be a dielectric material. Though generallyreflective, a metallic material may not be used to form the reflectivesecondary surface 40. Because the refractive index of a metallicmaterial is a complex number having real and imaginary components, theevanescent field 38 formed at each point of total internal refractiondoes not enable evanescent coupling of the light rays 32 as describedherein. Consequently, if the reflective secondary surface 40 was formedof a metallic material, the light rays 32 would not propagate as astanding wave toward the distal end 24 of the light pipe 20. Instead,the light rays 32 may be reflected off the reflective secondary surface40 and transmitted through the emitting portion 28 of the surface 26without traveling a desired distance through the light pipe 20 prior toemission.

The reflective secondary surface 40 may be formed by any suitableprocess that applies or disposes a dielectric material of higherrefraction index than the light pipe 20 adjacent at least the overlayportion 27 of the surface 26. In at least one embodiment according tothe present disclosure, the light pipe 20 may include a reflectivesecondary surface 40 that is formed by a two-shot molding process, wherethe reflective secondary surface 40 is molded onto the overlay portion27 of the surface 26 of a previously-molded light pipe 20 as shown inFIGS. 11A and 11B. Moreover, any suitable molding process may be used toform the reflective secondary surface 40 including, but not limited to,transfer molding, insert molding, multicolor molding, laminating, andthermoforming. In at least one embodiment, the reflective secondarysurface 40 may be formed by a printing process including, but notlimited to tampo-printing, pad printing, screen printing, painting,vapor deposition, hot stamping, or any other suitable process to formthe reflective secondary surface 40 described herein.

In at least one embodiment according to the present disclosure, thelight pipe assembly 10 may further include a reflective secondarysurface 40 formed by a combination of two or more processes. Forexample, in at least one embodiment as shown in FIG. 12, a first portion43 of the reflective secondary surface 40 may be formed by a printingprocess as described herein, and a second portion 45 of the reflectivesecondary surface 40 may be formed by a molding process as describedherein. The use of two or more processes to form the reflectivesecondary surface 40 may enable the formation of features not otherwisefeasibly formed using one process or another.

The light source 30 may be any suitable source of visible light thatincludes the desired wavelengths of light for a given application. In atleast one embodiment of the present disclosure, the light source 30 maybe one or more light emitting diodes. In at least one embodiment, theone or more light sources 30 may be either a red, amber, or white lightemitting diodes complying with the regulated color requirements of theUnited States Federal Motor Vehicle Safety Standard 108 or comparablecolor regulations of other jurisdictions.

The light source 30 may be optically coupled with the light pipe 20 byvarious means. In at least one embodiment, the proximal end 22 of thelight pipe 20 may include a flat profile adjacent the light source 30.In at least one embodiment, the proximal end 22 of the light pipe 20 mayinclude coupling optics engineered to efficiently transfer light rays 32into the light pipe 20. In at least one exemplary embodiment, couplingoptics may increase the transfer efficiency 5-7% compared to a flatprofile proximal end 22. In at least one embodiment, the proximal end 22may be angled to match the numerical aperture of the geometry of thelight pipe 20 to further improve transfer efficiency. In at least oneexemplary embodiment, a contrast ratio of less than or equal to 1.5 maybe obtained using a 27 in. light pipe 20 at 50-55% efficiency, where thelight pipe assembly 10 emitted about 30 lumens (lm) using a 56 lm lightsource 30.

In at least one embodiment according to the present disclosure, thelight pipe assembly 10 may further include a lens 50 surrounding atleast a portion of the emitting portion 28 of the surface 26 as shown inFIG. 13. The lens 50 may be formed with a plurality of lens opticalelements 52 formed in and across at least a portion of a surface 54 ofthe lens 50. In at least one embodiment, the lens 50 may include anytype of lens optical elements 52 including, but not limited to, Fresnel,flute, pillow, reflex, or any other suitable optic configuration. Thelens 50 with the plurality of lens optic elements 52 may be formed toenable the desired functional light distribution and the intensity anduniformity of the emitted light distribution emitted from the light pipe20 to further enable the desired lit appearance of the light pipeassembly 10.

The optical light pipe assembly 10 may be implemented in variousapplications to enable a uniform lit appearance. By way of non-limitingexample, in at least one embodiment, the light pipe assembly 10 may beused in an automotive lamp having a lens and a housing to provide avehicle's tail lamp function and a desired appearance, which mayintegrated into the styling theme of the vehicle. Likewise, the lightpipe assembly 10 may be used in an automotive applique lamp andintegrated into the styling theme of the vehicle. In one exemplaryembodiment, the light pipe assembly 10 may be particularly suited for apark function automotive lamp. In one exemplary embodiment, the lightpipe assembly 10 may be implemented in a center high-mounted stop lamp.Where light pipe assembly 10 is used within the housing and the lens ina lamp assembly, the lens may include lens optical elements, similar tothe plurality of lens optical elements 52, including, but not limitedto, Fresnel, flute, pillow, reflex, or any other suitable opticconfiguration.

While various embodiments of optical light pipe and methods for usingand constructing the same have been described in considerable detailherein, the embodiments are merely offered by way of non-limitingexamples of the disclosure described herein. It will therefore beunderstood that various changes and modifications may be made, andequivalents may be substituted for elements thereof, without departingfrom the scope of the disclosure. Indeed, this disclosure is notintended to be exhaustive or to limit the scope of the disclosure.

Further, in describing representative embodiments, the disclosure mayhave presented a method and/or process as a particular sequence ofsteps. However, to the extent that the method or process does not relyon the particular order of steps set forth herein, the method or processshould not be limited to the particular sequence of steps described.Other sequences of steps may be possible. Therefore, the particularorder of the steps disclosed herein should not be construed aslimitations of the present disclosure. In addition, disclosure directedto a method and/or process should not be limited to the performance oftheir steps in the order written. Such sequences may be varied and stillremain within the scope of the present disclosure.

1. A light pipe assembly, comprising: a light pipe extending from aproximal end to an opposing distal end and defining a surface comprisingan emitting portion and an overlay portion, the light pipe comprising amaterial capable of transmitting light with a first refractive index;and a reflective secondary surface comprising a second refractive indexgreater than the first refractive index, the reflective secondarysurface disposed adjacent the overlay portion of the light pipe.
 2. Thelight pipe assembly of claim 1, wherein the reflective secondary surfacecomprises a non-metallic material capable of reflecting light.
 3. Thelight pipe assembly of claim 1, wherein the reflective secondary surfaceis disposed adjacent the overlay portion such that a gap is formedbetween the reflective secondary surface and the light pipe, the gapselected such that the reflective secondary surface can propagate anevanescent wave at a point where any of a plurality of light raystraveling through the light pipe are internally reflected at a boundarybetween the overlay portion and reflective secondary surface.
 4. Thelight pipe assembly of claim 3, wherein the gap is variable along alength of the light pipe.
 5. The light pipe assembly of claim 1, whereinthe width of the reflective secondary surface varies along a length ofthe light pipe.
 6. The light pipe assembly of claim 5, wherein the lightpipe comprises a bend, and wherein the reflective secondary surface isnarrower at or near the bend than at a location adjacent thereto.
 7. Thelight pipe assembly of claim 1, further comprising: at least one firstlight source disposed adjacent the proximal end of the light pipe andcapable of generating a plurality of light rays generally directed intothe light pipe in a direction of the distal end.
 8. The light pipeassembly of claim 7, further comprising: at least one second lightsource disposed adjacent the distal end of the light pipe and capable ofgenerating a plurality of light rays generally directed into the lightpipe in a direction of the proximal end.
 9. The light pipe assembly ofclaim 8, wherein at least one of the at least one first light source andthe at least one second light source is a light emitting diode.
 10. Thelight pipe assembly of claim 1, wherein the overlay portion of the lightpipe comprises a cross-sectional area having a first shape and theemitting portion of the light pipe comprises a cross-sectional areahaving a different, second shape.
 11. A lamp assembly, the lamp assemblycomprising: a light pipe assembly, comprising: a light pipe extendingfrom a proximal end to an opposing distal end and defining a surfacecomprising an emitting portion and an overlay portion, the light pipecomprising a material capable of transmitting light with a firstrefractive index; and a reflective secondary surface comprising a secondrefractive index greater than the first refractive index, the reflectivesecondary surface disposed adjacent the overlay portion of the lightpipe; at least one light source disposed adjacent the proximal end ofthe light pipe and capable of generating a plurality of light raysgenerally directed into the light pipe in a direction of the distal end;a housing; and a lens disposed adjacent the housing such that the lensand housing substantially surround the at least one light source, thelight pipe, and the reflective secondary surface.
 12. The lamp assemblyof claim 11, wherein the reflective secondary surface comprises anon-metallic material capable of reflecting light.
 13. The lamp assemblyof claim 11, wherein the reflective secondary surface is disposedadjacent the overlay portion such that a gap is formed between thereflective secondary surface and the light pipe, the gap selected suchthat the reflective secondary surface can propagate an evanescent waveat a point where any of a plurality of light rays traveling through thelight pipe are internally reflected at a boundary between the overlayportion and reflective secondary surface
 14. The lamp assembly of claim13, wherein the gap is variable along a length of the light pipe. 15.The lamp assembly of claim 11, wherein a width of the reflectivesecondary surface is wider at or near the distal end than at or near theproximal end of the light pipe.
 16. The lamp assembly of claim 11,wherein the overlay portion of the light pipe comprises across-sectional area having a first shape and the emitting portion ofthe light pipe comprises a cross-sectional area having a different,second shape.
 17. The lamp assembly of claim 11, further comprising atleast one additional light source disposed adjacent the distal end ofthe light pipe and capable of generating a plurality of light raysgenerally directed into the light pipe in a direction of the proximalend.
 18. The lamp assembly of claim 11, wherein the at least one lightsource is a light emitting diode.
 19. A light pipe assembly, comprising:a light pipe extending from a proximal end to an opposing distal end anddefining a surface comprising an emitting portion and an overlayportion, the light pipe comprising a material capable of transmittinglight with a first refractive index; and a reflective secondary surfacecomprising a second refractive index greater than the first refractiveindex, the reflective secondary surface disposed adjacent the overlayportion of the light pipe; and at least one first light source disposedadjacent at least one end of the proximal end and the distal end of thelight pipe and capable of generating a plurality of light rays generallydirected into the light pipe from the at least one end; wherein thereflective secondary surface comprises a material selected from thegroup consisting of a non-metallic material capable of reflecting lightand a dielectric material capable of reflecting light.
 20. The lightpipe assembly of claim 19, wherein the reflective secondary surface isdisposed adjacent the overlay portion such that a gap is formed betweenthe reflective secondary surface and the light pipe, the gap selectedsuch that the reflective secondary surface can propagate an evanescentwave at a point where any of a plurality of light rays traveling throughthe light pipe are internally reflected at a boundary between theoverlay portion and reflective secondary surface.